Combustion liner cooling slot stabilizing dimple

ABSTRACT

A combustor liner film cooling slot, of the variety including an annular space extending circumferentially of the liner which space is defined between overlapping portions of telescoping liner segments, a cooling fluid plenum substantially circumscribing the liner, means for transferring cooling fluid from the plenum to the space, means for exhausting fluid from the space onto the liner, and an overhanging lip extending substantially axially downstream of the space for facilitating attachment of the fluid to the liner in a protective film barrier, is provided with a plurality of circumferentially spaced stabilizing dimples disposed within the overhanging lip. Each dimple includes a radially depressed portion which has a larger circumferential width at its upstream extremity than its downstream extremity. The depression is disposed toward the associated cooler liner segment and is provided with a geometry which enhances stress relief of the lip as well as cooling fluid attachment as a protective film barrier upon the heated side of the liner downstream from the lip.

United States Patent [191 Smuland et al. it

' n11 3,826,082 [45] .July 30,1974

[ COMBUSTION LINER COOLING SLOT STABILIZING DIMPLE Inventors: Robert J.Smuland, Fairfield;

Richard K. Ward, Maineville, both of Ohio 7 General Electric Company,Cincinnati, Ohio Filed: Mar. 30, 1973 Appl. No.: 346,595

Assignee:

US. ci..; 60/39.65, 60/39.66

Int. Cl. F02c 7/18 Field of Search.... 60/3965, 39.66

[56] References Cited UNITED STATES PATENTS j 3/1967 Macauley et al.60/3966 3,589,]27 6/l97l' Kenworthy et al. 60/3965 X 3,745,766 7/1973Melconian ..60/39.65X 1, 5.l19l9MQ2@ SYEFY 3.35":H :1

FOREIGN PATENTS OR APPLICATIONS 141,858 9/1948 Australia 60/39.65

Primary Examiner-Carlton R. Croyle Assistant ExaminerRobert E. GarrettAttorney, Agent, or Firm-James M. Kipling; Derek P. Lawrence [57]ABSTRACT A combustor-liner film cooling slot, of the variety includingan annular, space extending circumferentially' of the liner which spaceis defined between overlapping portions of telescoping liner segments, acooling fluid plenum substantially circumscribing the liner, means fortransferring cooling fluid from the plenum to the space, means forexhausting fluid from the space onto the liner, and an overhanging lipextending substantially axially downstream of the space for facilitatingattachment of the fluid to the liner in a protective film'barrier, isprovided with a plurality of circumferentiallyspaced stabilizing dimplesdisposed within the overhanging lip. Each dimple includes a radiallydepressed portion which has'a larger circumferential width at itsupstream extremity than its downstream extremity. The depression isdisposed toward the associated cooler liner segment and is provided witha geometry which enhances stress relief of the lip as well as coolingfluid attachment as a protective film barrier upon the heated side ofthe liner downstream from the lip.

9 an TDFZY PS, Fi ure- PAIENTED SHEET 20F 2 .EUH?

COMBUSTION LINER COOLING SLOT STABILIZING DIMPLE BACKGROUND OF THEINVENTION This invention relates to combustion chambersand, moreparticularly, to means for effecitively cooling combustion chambers. Thepresentinvention will be discussed in the environment of combustionchambers from a plurality of individual jets, corresponding to the 5individual apertures, into a flow having substantially uniformcircumferential velocity.

While theextended overhanging lip has performed well with respect toavoiding aspiration and providing attachment, there has been anunfortunate structural for use in gas turbine engine; however, theconcepts of repercussion in this design in that, under the thermal thisinvention are broadly applicable to any situation wherein similarcombustion chambers are utilized.

The invention herein described was made in the course of or under acontract, or a subcontract thereunder, with the United States Departmentof the Air Force.

Development of high temperature operating cycles within gas turbineengines has put increased emphasis upon the development of combustionchambers capable of withstanding-extremely high temperatures. Im-

provements in liner alloys and other combustion chamber materials hasaided in this quest. To further enhance combustion chamberdependability, efficient and reliable means for cooling combustionchambers are necessary.

To date, the most efficient combustion chamber cooling techniques haveinvolved, in part, the forrnation of aprotective film boundary of coolair or other cooling fluid between the hot gases of combustion and theliner portions forming and defining the combustion zone. Typically, acombustion chamber liner defining a combustion zone also partiallydefines a cool fluid plenum usually circumscribing the combustion zone.Means are commonly provided for transferring a portion of the cool fluidfrom the plenum into the combustion zone to form the protective filmbarrier from the hot combustion products in the chamber.

lnorder to accomplish effective film propagation,- means must beprovided for directing the fluid in a film upon the liners inner orheated surface. This means must efiectively perform attachment (that is,the disposition of the fluid in a low-turbulence boundary layerimmediately adjacent the liner to be protected) without aspirating orentraining hot gases from the combustion zone. Such entrainment wouldnegate the effectiveness of the film cooling by creating a turbulentinterchange whereby hot gases of combustion would directly impinge onthe liner.

' Effective attachment requires substantially uniform and low cool fluidvelocity from the source of the fluid circumferentially about the'linerin order to avoid turbulence as well as localized hot streaks or hotspots which arise in the absence of adequate film protection. At thesame time, the means for transferring the cool fluid from thesurrounding plenum to the liner has, in

the past, commonly taken the form of a plurality of spaced aperturescircumferentially disposed about the stresses associated withcombustion, the lip has become warped and structurally incapable ofcontinuing its proper function. The reason for this undesirablesituation is that thermal gradients imposed upon the liner skin canoperate upon residual material stresses to cause localized closure ofthe cooling slot (that is, a

bending and buckling of the overhanging lip into engagement with theassociated liner to block flow near thepoint of engagement) with aresultant interruption of cooling flow. This can cuase heat damage tothe unprotected liner portions and resultant accelerated detspaced,conical dimples. The dimple provides mechanical support to prevent lipclosure as wellas enhancing the flexibility of the lip. The flexibledimples further provide a means for absorbing thermal stresses withoutbuckling. Such a configuration provides a significant life increase overthe non-dimpled lip. However, long term usage is hampered by stresslevels in the conical dimple which may result in fatigue cracking sincethe shape of the dimple concentrates thermal stress at the apexof thecone. In addition, this form of dimple ere ates an aerodynamicdisturbance which reduces the film cooling effectiveness downstream ofthe dimple.

The present invention provides an improvement.

BRlEF SUMMARY oF THE lNVENTlON It is, therefore, a principal object ofthe present invention to provide a combustor liner film cooling slothaving a reinforced overhanding lip with improved life and film coolingcharacteristics.

In order .to accomplish this and other objects, which will becomeapparent from the detailed description hereinafter, the presentinvention, .in one embodiment thereof, provides a combustion chamberliner which comprises a number of telescoping, partially overlappingsegments. A cooling fluid plenum substantially circumscribes the liner,and means are provided for transferring cooling fluid from the plenum toan annular space defined between adjacent overlapping liner seg ments.The radially inner of the overlapping segments I forms an overhanginglip extending substantially axially downstream of the space whichfacilitates attachment of the fluid to the liner in a protective filmbarrier. This lip is provided with a plurality of circumferentiallyspaced stabilizing dimples, each dimple including a radially depressedportion which has an upstream, substantially linear extremity (orjunction with the lip surface) and a downstream arcuate extremity, whichoccurs at the downstream edge of the lip. Each dimple has a larger widthin the circumferential direction at its upstream extremity than at itsdownstream extremity. Furthermore, each dimple departs from the lipsurface to a first depth near its upstream extremity and to a seconddepth near its downstream extremity, the second depth being greater thanthe first. Each dimple also includes lateral extremities at the junctionof the depressed portion with the lip surface, the lateral extremitiesof any one dimple converging in the downstream direction. As a result,the adjacent of the lateral extremities of adjacent dimples diverge inthe downstream direction. Finally, the depression extends in thedirection of the associated liner segment.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be madeclearer by reference to the following description taken together withthe appended drawings wherein:

FIG. 1 is a simplified cross-sectional view of a cornbustion chamber ofa gas turbine engine employing cooling slots,

FIG. 2 depicts'a cross-sectional view of areinforcing dimple accordingto the prior art;

FIG. 3 illustrates a pictorial view of the prior art dimple of FIG. 2taken along line 3-3;

FIG. 4 shows a cross-sectional view of a cooling slot according to thepresent invention;

FIG. 5 is a pictorial view taken along line 4-4'of FIG. 3 and showingdetails of the reinforcing dimple of the present invention;

FIG. 6is a graphical representation of stress levels in prior art anddimples according to the present invention; and

FIG. 7 is a graphical representation of comparative aerodynamicefficiencies.

DETAILED DESCRIPTION OFA PREFERRED EMBODIMENT 40 for the purpose ofdefining a radially inner cooling fluid plenum 42. The combustion zoneitself is designated 44 and is defined by liners 34 and 40 as well as byan upstream dome 46 which cooperates with a fuel nozzle 48 through fuelfor combustion is directed into the combustion zone. An air/fuel inlet50 is defined between axial extensions 52 and 54 of liners 34 and 40,respectively.

In general operation, the combustion chamber described is substantiallysimilar to those in present use. A flow of atmospheric air ispressurized by means of a compressor (not shown) upstream of thecombustion zone 44 with the compressor discharge directed partially intoplena 52 and 54 as well as into the fuel/air inlet 50. A quantity offuel is mixed with the portion of air entering fuel/air inlet 50 and isignited within combustion zone 44. The rapid expansion of the burninggases and the configuration of liners 34 and 40 results in the. gasesbeing forced from combustion zone 44 serves to drive the upstreamcompressor through an interconnecting shaft. The remaining energy of thegas stream provides energy for driving thrust toward the left in FIG. 1.

' The cooling of liners 34 and 40 is the subject of the presentinvention, and will be described with respect to the remaining figures;FIG. 2 illustrates a crosssectional view of a cooling slot according tothe prior art. FIG. 3 is a view of this same slot taken along line 3-3of FIG. 2 and further particularizes the cooling slot of the prior art.Referring back to FIG. 1, liner 34 may be seen to be dividedsubstantially into a number of axially adjacent segments. A typicalsegment 60 can beseen to be in telescopic cooperation with a typicalsegment 62? downstream thereof by means of a junction designatedgenerally by the numeral 64'. At this junction is disposed a coolingslot configuration which, in substance, comprises a cooling filmpromoter for passing cool fluid from plenum 36' in a protective filmbarrier upon liner 34, the latter liner partially defining a hot gaspassage (the combustion zone 44). The segment 60 can be seen topartially define the plenum 36 as well as the. combustion zone 44'.Segment 62' likewise partially defines the plenum and the hot gaspassage, and these liner segments cooperate to form an annular space 66'extending circumferentially of the liner between them. The space 66'.includes asubstantially closed upstream end 70f and a downstream-facingopen end or exit 68'. Thus, the space is substantially isolated from thecombustion zone except for communication through exit 68.

As can be seen in FIG. 1, the annular space 66 is disposed between aportion of downstream segment 62' and an xial extension of the upstreamsegment 60' of liner 34'. It can further be seen that the space 66' isconnected to the surrounding plenum 36 by means of a plurality ofcircumferentially spaced apertures 74' through a portion of the liner.It is the function of these apertures to deliver cool fluid from theplenum to the space. 66 and therefrom to the heated portions of com-'bustion liner 34' for the formation of a protecivefilm barrier.-Aprerequisite to the formation of such a film barrier is that the coolfluid which is intended to form the barrier be free of large velocitygradients in the circumferential direction, which gradients could leadto aspiration of hot gases thus adversely affecting the benefits of thebarrier.

It would, therefore, be beneficial to the barrier formationto provideamore uniform means for delivering cool fluid to the space than theplurality of apertures 74'. However, the cool fluid quantity must bemetered, and these apertures are a most effective means foraccomplishing metering. In addition, the structural forces imposed uponthe liner require that it be formed in a particularly strong fashion. Amore uniform delivery system, such as a continuous annular slot betweenthe plenum 36 and space 66 would substantially weaken the liner incomparison to apertures 74.'I-Ience, the apertures are a preferreddelivery mechanism.

But, yet, the apertures do serve to transfer the fluid to the space 66in a plurality of spaced jets with subthrough an outlet 56 and intoengagement with a turbine 58. Rotary portions of the turbine are drivenby this exiting fluid and -a portion of the energy thereof stantialcircumferential velocity gradients therebetween. There must, then, beprovided means for allowing acoalescence of these velocities prior tothe direction of the fluid onto the combustor linerfor the purpose offorming a barrier. To this end, the overhanging lip 72 extends asubstantial distance downstream of the junction 76' between linersegments 60' and 62. Thus, the space 66' is given a substantial axiallength. By reason of this length, the fluid passing from plenum 36' in aplurality of jets through apertures 74' is given a predetermined periodof residence within space 66' as it passes downstream therein. Duringthis time, the viscous forces within the fluid and frictional engagementthereof with the surfaces of the lip 72' and downstream liner segment62' cause the fluid to develop a more uniform circumferential velocity.In order to achieve the desired amount of velocity equalization, thespace 66 must be substantial in length and, hence, the overhanging lip72 must likewise extend axially downstream for a substantial distance.In this way, the overhanging lip 72 serves to facilitate the attachmentof the cool fluid to the liner in a protective film barrier.

ential width 94 proximate its upstream extremity than circumferentialwidth 96 proximate its downstream extremity. In addition,'it can be seenthat the dimple extends to and terminates in the'downstream edge 72a oflip 72.

Referring to FIG. 4, it is therein illustrated that the depressedportion 92 of the dimple extends radially from the surface of lip' 72 inthe direction outwardly of the center of the combustion zone and towardthe associated downstream liner segment 62. The depressed portiondepartsfrom the surface of the lip to a first depth near its upstream extremityand to a second and greater depth near its downstream extremity. Inother words, the depressed portion of the dimple converges toward thedownstream liner segment 62 in the downstream direction.

But, at the same time, the axial length of the lip is suchthat-residualstresses within the structure defining the lip combinewiththerr'nal stresses resulting from the heat of combustion withinchamber 44' to cause structural deformation of the lip that can resultin local closing of the exit 68', through which the cool fluid isnormally exhausted from the space onto the liner. Should this occur,localized hot streaks would develop wherein cooling fluid filmprotection would fail. This, in turn, could result in local damage to ordestruction of the combustion chamber liner;

- In order to strengthen the overhanging lip 72' against such stresses,as well as relieve the residual stresses therein, there have beenprovided in the past a plurality of reinforcing dimples within thematerial of the lip itself. Such dimples, as stated, are illustrated inFIGSJZ and 3. In these figures, the dimples are designated 80, and canbe seen to be substantially conical in the cross section, originating ina point 82 at their upstream ends andterminating in a substantiallycircular cross section 84 at theirdownstream ends. The dimplesare formedas depressions in the .lip material itself, with the depressionextending in the direction from the lip surface toward the associateddownstream liner segment 62 (and, hence, away from the centerline of thecombustion zone). The lateral extremities86 and 88 of an individualdimple comprise the intersections between the conical cross section ofthe depression and the plane of lip 72. These lateral extremitiesdivergein the downsteam direction with respect to any individual dimple;

and, contemporaneously, the adjacent lateral extremities of adjacentdimples converge in the downstream direction. These prior art dimpleshave been found to improve operational reliability of the overhanginglips associated therewith in that the lip is strengthenedagainstdeformation and local'exit closure. However, these dimplesprovide stress concentrations and result in fatigue cracking whensubjected to long-term use. In

addition, the dimple configurations create an aerodynamic disturbancewhich reduces film cooling effectiveness downstream of the dimple.

The present invention comprehends the usefulness of dimples asreinforcing means for overhanging lips, but overcomes the principalobjections thereto in theprior art. FIGS. 4 and 5 depict reinforcingdimples according to the present invention and their cooperation withthe overhanging lip and associated cooling slot structure. As may beseen from FIG. 5', each dimple, designated 90, includes a substantiallyradially depressed portion 92, this portion having a substantiallylarger circumfer- In the particular embodiment depicted in FIGS. 4 and5, the upstream extremity 98 of each dimple is substantially linear inthe circumferential direction with respect to the lip, while the'downstreamfextremity is substantially arcuate describing an arc 100 inthe cross pressed portion 92 from. greater width upstream at 94 tosmaller downstream width-96. As a result of this latter characteristic,the lateral extremities 102 and 104 -of individual dimples converge inthe downstream direction while the adjacent extremities of adjacentdimples diverge in the downstream direction.

It has been found experimentally that the reinforcing dimple of thepresent invention thus described serves to increase the. life of theoverhanging lip and, hence, the reliability of the associated combustorliner over extended periods of applicationQOne facet of this improvementrests in a substantial increase in overall fatigue strength due toreduction in the localized stresses in the lip structure proximate thedimple. This improvement is dramatically exemplified in FIG. 6 whichdisplaysa graphical representation of stress versus position overvarious stations through dimples according to the prior art and presentinvention. It can be appreciated frornthis Figure that localstressesaregenerally maintained at levels approximately one-half of the magnitudeof the prior art dimple by means of utilization of the presentinvention. Experiments have illustrated that this stressreductionresults in a life gain of on a ratio of 15 to 1 over the priorart cooling slot.

An additional benefit of the present invention relates to the efiiciencywith which the cooling fluid operates to remove heat from the combustionchamber liner. This can be expressed in terms of cooling filmeffectiveness, 1 which is depicted in graphical form in FIG. 7 andplotted versus axial distance downstream of the dimple along'the linersurface. The figure illustrates a comparison in efficiency between theprior art dimple andthe dimple according to the present invention, bothdirectly downstream of individual dimples and inthe areas betweendimples downstream thereof. As the figure discloses, a markedimprovement infilm barrier effectiveness is achieved by utilization ofthe dimples according to the present invention. This improvement can betraced'to aerodynamic improvements of the present dimple configurationwhich cause the film flow streamlines to converge and, thus, minimizedisturbance or wake effects downstream of the dimples.

It has been illustrated that the present invention results not only insignificant life improvements but also in cooling improvements and theefficiency thereof with respect to gas turbine engines to which thepresent invention is applied. Numerous variations of the particularembodiment disclosed can be made without departing from the spirit ofthe invention. For example, neither the lateral nor the upstreamextremities of the dimples need be linear so long as theinterrelationship therebetween is maintained. Similarly, the downstreamextremity of the dimples need not necessarily be arcuate. Othervariations will occur to those skilled in the art which also do notdepart from the spirit of the invention. It is intended that all suchvariations be within the scope of the appended claims. v

What is considered to be new and desired to be secured by Letters Patentof the United States is:

1. In a combustor liner film cooling slot of the variety including anannular space extending circumferentially of the liner and definedbetween overlapping portions of telescoping liner segments, a coolingfluid plenum.

stream extremity, the first width beinggreater than the second.

2. The improvement of claim 1 wherein said lip terminates in adownstream edge, and said dimple extends to said edge.

3. The improvement of claim 1 wherein said depressed portion departsfrom the surface of said lip to a first depth proximate its'upstreamextremity and to a second depth proximate its downstream extremity, saidseconddepth being greater than the first.

4. The improvement of claim 1 wherein said upstream extremity of saiddepressed portion is substantially linear and said downstream extremitythereof is substantially arcuate.

5. The improvement of claim 1 wherein said depresssed portion furtherincludes lateral xtremities, and said lateral extremities substantiallyconverge in the downstream direction. I I

6. The improvement of claim 5 further including a plurality of saiddimples so characterized, said dimples spaced circumferentially aboutsaid lip.

7. The improvement of. claim 6 wherein adjacent of the'lateralextremities of adjacent dimples substantially diverge in the downstreamdirection.

8. The improvement of claim 7 wherein said depressed portion of each ofsaid dimples departs from the surface of said lip to a first depthproximate its uppressed portion extends radially toward said liner.

1. In a combustor liner film cooling slot of the variety including anannular space extending circumferentially of the liner and definedbetween overlapping portions of telescoping liner segments, a coolingfluid plenum substantially circumscribing the liner, means fortransferring cooling fluid from the plenum to the space, means forexhausting fluid from the space onto the liner, and an overhanging lipextending substantially axially downstream of the space for facilitatingattachment of the fluid to the liner in a protective film barrier, theimproveMent comprising: a stabilizing dimple disposed within said lip,the dimple including a substantially radially depressed portion, thedepressed portion having a first circumferential width proximate itsupstream extremity and a second circumferential width proximate itsdownstream extremity, the first width being greater than the second. 2.The improvement of claim 1 wherein said lip terminates in a downstreamedge, and said dimple extends to said edge.
 3. The improvement of claim1 wherein said depressed portion departs from the surface of said lip toa first depth proximate its upstream extremity and to a second depthproximate its downstream extremity, said second depth being greater thanthe first.
 4. The improvement of claim 1 wherein said upstream extremityof said depressed portion is substantially linear and said downstreamextremity thereof is substantially arcuate.
 5. The improvement of claim1 wherein said depresssed portion further includes lateral xtremities,and said lateral extremities substantially converge in the downstreamdirection.
 6. The improvement of claim 5 further including a pluralityof said dimples so characterized, said dimples spaced circumferentiallyabout said lip.
 7. The improvement of claim 6 wherein adjacent of thelateral extremities of adjacent dimples substantially diverge in thedownstream direction.
 8. The improvement of claim 7 wherein saiddepressed portion of each of said dimples departs from the surface ofsaid lip to a first depth proximate its upstream extremity and to asecond depth proximate its downstream extremity, said second depth beinggreater than said first depth.
 9. The improvement of claim 8 whereinsaid depressed portion extends radially toward said liner.